We are soldering a 8 pin TTL chip on to a CEM1 board that has a hot air level soldering. We use no clean soler paste for the reflow process. Now the customer wants us to clean since he is afraid of flux attracting the dust. We have some SMT LEDs that have a plastic casing and hence cleaing with IPA is the only soultion. But soon after cleaning and drying with IPA, we find a white residue formation. How do we avoid this white residue? Our problem is that the custmer insists on cleaning after use of no clean solder paste. Can we use IPA on a ultrasonic cleaner? Is there any other cleanres available that doe snot affect the plastic casings of SMT LEDs?

>But soon after cleaning and drying with IPA, we find a white residue formation. A: IPA will not nothing to clean your board. The white residue is exactly what you should expect. Search the fine SMTnet Archives for background.

>How do we avoid this white residue? A: If you want to avoid the white residue, stop using IPA. Your IPA is probably 50% water. Water will turn the residues of most "low residue fluxes" a cloudy, white color.

>Is there any other cleanres available that doe snot affect the plastic casings of SMT LEDs? A: Can't talk to your LEDs, but many people cleaning low res flux residues from boards use a saponifier. Saponifiers convert the flux residue to a soap, which you can wash from the board with water. We think good saponifiers suppliers are: * Kyzen * Envirosense

Mike Konrad has commented on the saponifiers that he likes in previous SMTnet threads and he'll certainly join-in shortly.

Other saponifier suppliers are: * Prozone * Axarel

If you want to do this down and dirty, using Cascade in agitation with your ultrasonic cleaner will probably remove the NC flux residue. Continuing points on this are: * Cleaning the Cascade residue from your boards is another story. * Ultrasonic cleaning assembled boards could damage components on your board. Search the fine SMTnet Archives for background discussion.

How about taking a deep breath? Assuming your customer is certain that they don't want NC flux res on their boards, consider: * Sending this current batch of NC flux res boards to a contract cleaning shop * Converting the process for on-going product to water soluable flux residues

Dave is correct. No-clean flux + water = white residue (unless the proper chemical is mixed with the water). Additionally, no-clean flux + IPA = white residue. Many saponifiers work well as do other cleaning agents. White residue may also be a result of profile issues (usually too hot).

I do not understand why you are concerned about LED�s. LED�s are frequently cleaned using a water-based cleaning process.

I can recommend specific cleaning chemicals but keep in mind that a chemical must be compatible with a specific cleaning machine.

Here are some chemical recommendations. Please keep in mind that not all chemicals are compatible with all cleaning systems.

White residues are a common problem when cleaning no-clean fluxe residues. The white residue forms when the flux residue is partialy removed, etc. Alcohol should not be your only solution for cleaning. In general, solvents may attack some plastic parts and inks so I prefer a water based chemistry for cleaning. I personally use Kyzen A4406E at 120 degrees F. in a spray washer (modified AAT) and it cleans great. This chemistry has mild saponification and does need to be rinsed. I rinse with heated DI water for 1 minute in the same washer.